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the plumes suggests that hydrocarbons have migrated preferentially <br /> along high-permeability axial zones of the channel deposits, rather <br /> than directly down the groundwater gradient, which is oriented <br /> north-south rather than northeast-southwest. It appears that the <br /> permeability to hydrocarbons is less than the permeability to <br />' uncontaminated groundwater, thereby slowing the southward migration <br /> of contaminants. <br /> 5. 0 REMEDIATION ALTERNATIVES <br /> When considering remediation alternatives for both soil and <br /> I groundwater, several conditions must be met. It is important to <br /> employ remedial methods that are effective, affordable, and <br /> environmentally safe. Other factors that must be considered include <br /> on-site safety and minimizing disruptions of the normal operations <br /> of the site. <br /> 5 . 1 Soil Remediation <br /> To remediate the soil at the site, three alternatives were <br /> considered: excavation and disposal or on-site treatment; in-situ <br /> vapor extraction; and in-situ bioremediation. The following <br /> sections briefly discuss the theory, feasibility, cost and <br /> estimated time of completion for each method. <br /> 5 . 1. 1 Excavation <br /> Excavation is a fast and effective method of site remediation where <br /> the contamination is shallow and distant from sensitive features. <br /> Once the contaminated soil has been removed from the excavation, it <br /> can be treated on-site or transported to an appropriate landfill <br /> facility. However, if transported, liability for the soil usually <br /> remains with the generator. Excavation is usually not feasible <br /> beyond a depth of 30 to 40 feet. <br /> Assuming that excavation to a depth of 35 feet could be undertaken, <br /> between 30 and 40% of the contaminated soil at the site could be <br /> removed for treatment or disposal. Due to the lateral spreading of <br /> soil contamination below 30 feet, more than 50% of the <br /> contamination is not accessible by normal excavation methods. The <br /> highest concentrations of hydrocarbons, at a depth of 20 to 25 <br /> feet, would be removed, but the secondary cell at 40 to 50 feet <br /> would probably be left in the ground. Excavation would probably <br /> I require several days to a few weeks, causing significant <br /> inconvenience to the property owner. GeoAudit does not regard <br /> excavation as a viable option for the site. <br /> 6 <br />